The present invention relates to an engine mounting applied to a motor-vehicle frame and in greater detail to an engine mounting adapted to damp low-frequency and large-amplitude vibrations and to insulate the frame from high-frequency and small-amplitude vibrations.
It is known that an engine mounting may be comprised of an envelope, an elastomeric diaphragm of truncated conical form, a pin, engagement parts connecting the envelope to the motor-vehicle frame.
The diaphragm is associated at its ends with the envelope side walls and in the middle with the pin designed to support the engine weight.
While the vehicle is running, when low-frequency and large-amplitude oscillations, that is between 5 and 10 Hz and 2 and 4 mm respectively, are present, due for example to bounds as a result of the road bumpiness, the elastomeric diaphragm is subject to an increasing deformation due to the dissipation of the energy absorbed in damping the oscillations.
Unfortunately, in the presence of high-frequency, between 100 and 200 Hz, and small-amplitude, between 50 and 200 micron, oscillations the elastomeric diaphragm behaves more or less like a spring the rigidity constant of which increases as the frequency increases, practically transmitting to the frame to a greater degree the oscillations received.
Therefore the known mounting does not insulate the frame from high-frequency and small-amplitude vibrations.
The preceding drawback can be solved having recourse to further known devices in which particular means is provided designed to reduce the values of the high-frequency and small-amplitude vibrations transmitted to the frame.
The known solutions are based on the principle of hydraulically damping low-frequency and large-amplitude vibrations and absorbing high-frequency and small-amplitude vibrations through the displacements of elastomeric diaphragms.
Practically these diaphragms of small thickness moved in opposite ways relative to the axis of the device by high-frequency and small-amplitude vibrations during their movement prevent high-frequency reactions from being transmitted to the frame or greatly attenuate their transmission.
By way of example we only mention here that such a device is disclosed in GB Patent 2 041 488 B.
However the previous solution involves the drawback of having recourse to particular closure means and modalities in order to ensure a perfect sealing of the liquid inside the device.
The problem that the applicant wished to solve during its research was how to accomplish an engine mounting capable of eliminating or at least substantially attenuating in a uniform manner the high-frequency and small-amplitude vibrations included between a determined range, resorting to the use of elastomeric materials and avoiding taking advantage of damping means in a liquid.
The solution to this problem must also ensure the integrity of the elastomeric materials so that the different stresses acting thereon may not give rise to breakages of any kind, for example as a result of tearings due to tractive efforts or high-frequency stresses of any other type which could tend to induce risks of fatigue relaxation in the elastomeric materials.
The present invention therefore aims at accomplishing an engine mounting which is devoid of all the previously mentioned drawbacks.